Certain tonalites of the broad crystalline core of Santa Lucia Range differ from the far more abundant normal granitic rocks of the region in that they are dark colored, invariably allotriomorphic, and consist largely of antiperthitic andesine, hypersthene, hastingsitic hornblende, ilmenite, and garnet. K-Ar determinations indicate the normal granitic rocks are Cretaceous, and there is moderate evidence that the charnockitic rocks formed in an earlier stage of the same plutonic cycle. The principal charnockitic pluton is intrusive, but the recrystallization of thin basic dikes that cut it shows that it acquired its charnockitic characters by late-igneous or subsequent processes. The metamorphic country rocks (Sur series) are of amphibolite facies elsewhere in the region, but they have been converted to granulite-facies assemblages in and locally near the pluton, whereas veins with granulite-facies minerals that formed at the same time as the pluton are not only concentrated around it but are typically less hydrous than the rocks in which they occur. The close genetic relation of these various rocks is indicated by the persistence of mineral species in rocks of various compositions, by the narrow range (1.0-1.2) of Fe/Mg in all the mafic minerals except garnet, and by the abnormally high values of Na/K and Fe''/Fe''' in both the pluton and the veins. The coarse-grained nature of the veins, the widespread occurrence of fracture-controlled alterations, and the appreciable metasomatism affected during the formation of the veins all indicate that the charnockitization was produced by fluids that passed through the solidified part of the pluton and out into the country rocks, chiefly along fractures opened by the intrusion.